Supplemental Executive Retirement Plans - Plan Details and Change in Benefit Obligation (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) payment	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Supplemental Executive Retirement Plans
Number of annual payments | payment			15
Change in Benefit Obligation
Benefit obligation at the beginning of the period	$ 17,556	$ 17,299	$ 19,214	$ 18,927
Service cost	98	84	196	168
Interest cost	121	164	242	329
Payments	(12)	(12)	(1,889)	(1,889)
Benefit obligation at the end of the period	17,763	$ 17,535	17,763	$ 17,535
Amounts Recognized in the Condensed Consolidated Balance Sheets:
Current accrued expenses and other current liabilities	1,913		1,913		$ 1,913
Non-current other liabilities	15,850		15,850		17,301
Total accrued liabilities	$ 17,763		$ 17,763		$ 19,214